1. Field of the Invention
This invention relates to apparatus for using the sun as a source of energy and more particularly to maintain a platform in a desired attitude with respect to rays of the sun used as a source of light energy.
2. Description of the Prior Art
It is known that electrical energy is usually derived from an energy source such as oil, a petroleum product. Recently, the cost of oil has been increasing because the availability of petroleum has been decreasing. The increasing cost of petroleum has caused extensive investigation of alternative sources of energy, such as the sun. Energy provided by the sun is referred to as solar energy.
Solar energy is usually converted into electrical energy by an array of solar cells carried upon a surface of a platform. The platform is mounted for rotation about first and second orthogonal axes substantially parallel to the earth's polar axis and to the platform surface, respectively. Because the first axis is parallel to the polar axis, the platform is referred to as being equatorially mounted.
The solar cells receive a maximum amount of solar energy when the rays of the sun are normal to the platform surface, thereby defining a desired attitude of the platform with respect to the rays of the sun. Therefore, during daylight it is desirable to maintain the desired attitude by moving the platform. During a day, the sun has an apparent position which undergoes major and minor components of change associated with a change of the time of day and a change of the time of year, respectively. Because the platform is equatorially mounted, the desired attitude is maintained by rotating the platform about the first axis in accordance with the major component of change and about the second axis in accordance with the minor component of change.
The platform rotates about the axes in response to signals from a photosensing unit comprised of four photocells of the type that provides a signal directly related to the quantity of received light. The photocells are arranged in two pairs disposed substantially along first and second orthogonal lines, respectively, on the surface. The first line is a projection of the first axis upon the surface; the second line is parallel to the second axis.
When the platform has the desired attitude, all of the photocells provide signals of substantially equal amplitude. In response to one of the pairs of the photocells providing a pair of signals of unequal amplitude, a motor rotates the platform about one of the axes in a direction that causes a reduction of the difference between the amplitudes of the signals, whereby the platform is substantially maintained in the desired attitude. By maintaining the platform in the desired attitude, the conversion of the solar energy has a minimized cost.
When the platform is located near a light reflecting object, reflected light may cause the platform to be in an undesired attitude where the solar cells do not receive the rays of the sun. It should be understood that light reflecting objects are commonplace in almost any environment where the platform is used. Additionally, in a hazy environment, the photocells may provide pairs of signals of equal amplitude when the platform is not in the desired attitude. The hazy environment is commonplace in many geographic areas. Accordingly, there is a need for a photosensing unit that maintains the platform in the desired attitude when the platform is located either near a light reflection object or in a hazy environment.